Jack,
   We also have a Breece Hill Q47 with 3 DLT4000 drives.  It is no longer
our primary robot, but it used to be.  It is true that a DLT7000 or DLT8000
drive should be able to read tapes written by a DLT4000 drive.  I *think*
it is true that ADSM will read these tapes also, but I do not have
first-hand experience on that.   New tapes that are written will be written
according to the format specified in the device class.  Check the
documentation on DEFINE DEVCLASS for more info - look for the section on
DLT drives.

   However - the main reason I am responding is the following.  When we
looked into upgrading our Q47 to DLT7000, we found that financially it did
not make sense.  This is because our robot, and drives, were not
differential SCSI.  In order to upgrade to DLT7000 drives, we would not
only have had to replace the drives, but we would have had to upgrade the
library itself to be differential SCSI.  The cost of this made it
financially not worth doing.  Instead, we opted to purchase a new larger
tape library.  I would look into whether your library is differential
already or not, and whether you would also run into this issue or
not.  Your library may indeed be differential.  I think the reason that
ours was not, was because we purchased it before Breece Hill offered a
differential version of the library.

   I believe that new data written to an existing tape, will be written in
the format that is already on that tape.  I believe that only newly written
tapes will be written at the higher density, and then only if you have the
device class defined properly.

..Paul
--
At 02:02 PM 11/1/2000 -0500, Palmadesso Jack wrote:
At 02:02 PM 11/1/2000 -0500, Palmadesso Jack wrote:
>  One of my libraries is getting close to maxing out its storage.  Its a
>Breece Hill Q47 with 3 DLT4000 drives.  I'd like to replace the drives with
>4 DLT8000 drives.  So far I've been hearing it should all be backward
>compatible but mostly thats just from the sales people.  Some of the people
>around here think a DLT4000 tape should be readable in 7000 or 8000 drive.
>Is this correct?
>
>If it is correct then is it possible to just replace the drives in the
>library redefine them to AIX and ADSM and continue on?  In other words will
>ADSM even notice?  We are running ADSM 3.1.2 L40 on an RS/6000.
>
>I am thinking it should be fine but I am mainly wondering how new data gets
>written back out to media?  Will new data being written to tape need to
>write on a scratch volume or can it just be written on a filling volume?
Or
>is all of this too much of a hassle and I should just buy a new library and
>migrate the data over to it?  Is there any sort of procedure defined
>someplace I could use?
>
>Thanks for any input
>Jack